Effect of adherence to primaquine on the risk of Plasmodium vivax recurrence: a WorldWide Antimalarial Resistance Network systematic review and individual patient data meta-analysis

Background Imperfect adherence is a major barrier to effective primaquine radical cure of Plasmodium vivax. This study investigated the effect of reduced adherence on the risk of P. vivax recurrence. Methods Efficacy studies of patients with uncomplicated P. vivax malaria, including a treatment arm with daily primaquine, published between January 1999 and March 2020 were identified. Individual patient data from eligible studies were pooled using standardized methodology. Adherence to primaquine was inferred from i) the percentage of supervised doses and ii) the total mg/kg dose received compared to the target total mg/kg dose per protocol. The effect of adherence to primaquine on the incidence of P. vivax recurrence between days 7 and 90 was investigated by Cox regression analysis. Results Of 82 eligible studies, 32 were available including 6917 patients from 18 countries. For adherence assessed by percentage of supervised primaquine, 2790 patients (40.3%) had poor adherence (≤ 50%) and 4127 (59.7%) had complete adherence. The risk of recurrence by day 90 was 14.0% [95% confidence interval: 12.1–16.1] in patients with poor adherence compared to 5.8% [5.0–6.7] following full adherence; p = 0.014. After controlling for age, sex, baseline parasitaemia, and total primaquine dose per protocol, the rate of the first recurrence was higher following poor adherence compared to patients with full adherence (adjusted hazard ratio (AHR) = 2.3 [1.8–2.9]). When adherence was quantified by total mg/kg dose received among 3706 patients, 347 (9.4%) had poor adherence, 88 (2.4%) had moderate adherence, and 3271 (88.2%) had complete adherence to treatment. The risks of recurrence by day 90 were 8.2% [4.3–15.2] in patients with poor adherence and 4.9% [4.1–5.8] in patients with full adherence; p < 0.001. Conclusion Reduced adherence, including less supervision, increases the risk of vivax recurrence. Supplementary Information The online version contains supplementary material available at 10.1186/s12936-023-04725-w.

Table S1.Studies included in analysis 7 Table S2.Reasons for studies not being included in analysis 9 Table S3.Studies targeted for the analysis but not included  S4.Comparison of baseline characteristics between included and targeted studies Table S5.Distribution (number and percentage) of patients in adherence categories by study for (A) supervision, (B) total mg/kg dose administered 17-18 Table S6: Risk factors for Plasmodium vivax recurrence between days 7 and 90 in patients with information on supervision Table S7.Sensitivity analyses for effect of adherence by supervision on Plasmodium vivax recurrence between days 7 to 90 restricted to randomised studies or observational studies Table S8.Sensitivity analysis for effect of adherence by supervision on Plasmodium vivax recurrence between days 7 to 90 Figure S4: Adjusted risk of recurrence between days 7 and 90 in patients with information on supervision Table S9: Demographic and baseline characteristics for adherence by total mg/kg dose administered Table S10.Risk factors for Plasmodium vivax recurrence between days 7 and 90 in patients with information on total mg/kg dose administered Table S11.Sensitivity analysis for effect of adherence by total dose (mg/kg) administered on P. vivax recurrence between days 7 to 90 Eligibility criteria 6 Specify inclusion and exclusion criteria including those relating to participants, interventions, comparisons, outcomes, study design and characteristics (e.g. years when conducted, required minimum follow-up).Note whether these were applied at the study or individual level i.e. whether eligible participants were included (and ineligible participants excluded) from a study that included a wider population than specified by the review inclusion criteria.The rationale for criteria should be stated.
Identifying studiesinformation sources 7 Describe all methods of identifying published and unpublished studies including, as applicable: which bibliographic databases were searched with dates of coverage; details of any hand searching including of conference proceedings; use of study registers and agency or company databases; contact with the original research team and experts in the field; open adverts and surveys.
Give the date of last search or elicitation.

10-12
Identifying studies -search 8 Present the full electronic search strategy for at least one database, including any limits used, such that it could be repeated.

Study selection processes 9
State the process for determining which studies were eligible for inclusion.10 Data collection processes 10 Describe how IPD were requested, collected and managed, including any processes for querying and confirming data with investigators.If IPD were not sought from any eligible study, the reason for this should be stated (for each such study).
10-12 If applicable, describe how any studies for which IPD were not available were dealt with.This should include whether, how and what aggregate data were sought or extracted from study reports and publications (such as extracting data independently in duplicate) and any processes for obtaining and confirming these data with investigators.

Data items 11
Describe how the information and variables to be collected were chosen.List and define all study level and participant level data that were sought, including baseline and follow-up information.• Use of a one-stage or two-stage approach.
• How effect estimates were generated separately within each study and combined across studies (where applicable).
• Specification of one-stage models (where applicable) including how clustering of patients within studies was accounted for.
• Use of fixed or random effects models and any other model assumptions, such as proportional hazards.
• Methods for quantifying statistical heterogeneity (such as I 2 and  2 ).
• How studies providing IPD and not providing IPD were analysed together (where applicable).
• How missing data within the IPD were dealt with (where applicable).

Exploration of variation in effects A2
If applicable, describe any methods used to explore variation in effects by study or participant level characteristics (such as estimation of interactions between effect and covariates).State all participant-level characteristics that were analysed as potential effect modifiers, and whether these were pre-specified.For each comparison and for each main outcome (benefit or harm), for each individual study report the number of eligible participants for which data were obtained and show simple summary data for each intervention group (including, where applicable, the number of events), effect estimates and confidence intervals.These may be tabulated or included on a forest plot.

15-18
Results of syntheses Present summary effects for each meta-analysis undertaken, including confidence intervals and measures of statistical heterogeneity.State whether the analysis was pre-specified, and report the numbers of studies and participants and, where applicable, the number of events on which it is based.
15-18 When exploring variation in effects due to patient or study characteristics, present summary interaction estimates for each characteristic examined, including confidence intervals and measures of statistical heterogeneity.State whether the analysis was pre-specified.State whether any interaction is consistent across trials.
Provide a description of the direction and size of effect in terms meaningful to those who would put findings into practice.

Risk of bias across studies
Present results of any assessment of risk of bias relating to the accumulated body of evidence, including any pertaining to the availability and representativeness of available studies, outcomes or other variables.Analyses statement from Jan 1, 1999, to March 3, 2020, in any language.In the analysis, we included prospective therapeutic efficacy studies including randomized and non-randomized therapeutic trials and prospective cohort studies with active follow-up.Studies on prevention, prophylaxis, reviews, animal studies, patients with severe malaria were excluded.Prospective clinical efficacy studies of uncomplicated vivax malaria with a minimum of 28 days of follow-up, daily primaquine (commenced before day 3) administered with schizontocidal treatments -chloroquine or artemisinin-based combination therapy, information on schizontocidal treatment dosing, supervision, timing, and dose of primaquine administered and planned per study protocol were included.The year of the study was taken as the year in which the paper was published, although the start and end date of patient enrolment were also recorded.Two independent investigators performed the review and identified relevant studies, resolving discrepancy through discussion.Principal       .. HR: hazard ratio, 95% CI: 95% confidence interval.* The assumption of proportional hazards held for the model by visual assessment for the adherence by supervision.# Patients with follow-up more than 7 days were considered in the Cox regression analysis.To examine the robustness of the parameter estimates, a sensitivity analysis was carried out by removing one study site at a time, which showed that the overall coefficient of variation for reduced adherence by supervision (50 versus 90) estimates in the multivariable model was minimal (appendix table S8). Malnutrition status -calculated for children aged<5 years of age (malnutrition status was missing for 77 patients in this analysis; 76 in 50 and one in 90).Data were missing for age (2 patients; one in 50 and one in 90), sex (one patient in 90), baseline parasitaemia (312 patients; 208 in 50 and 104 in 90), planned primaquine total dose (5 patients; 5 in 90), weight (795 patients; 733 in 50 and 62 in 90), baseline haemoglobin (1265 patients; 756 in 50 and 509 in 90), and fever (1128 patients; 599 in 50 and 529 in 90).# Patients with follow-up more than 7 days were considered in the Cox regression analysis.† Data were missing for sex (one patient; one in the 90), baseline parasitaemia (49 patients; 14 in 50 and 35 in the 90), fever (473 patients; 57 in 50, 15 in >50-<90 and 401 in the 90), weight (56 patients; 56 in 50), and baseline haemoglobin (232 patients; 58 in 50, 6 in >50-<90 and 168 in the 90).The adjusted HRs for age, sex, and parasitaemia are presented for the total mg/kg dose model assumes constant HR over follow-up period.* The effect of study sites was not assessed due to collinearity with adherence.The proportional hazards assumption did not hold on visual inspection of the exposure of interest, adherence by total mg/kg dose.To examine the robustness of the parameter estimates, a sensitivity analysis was carried out by removing one study site at a time, which showed that the overall coefficient of variation for levels of ad herence estimates in the multivariable model were small (Appendix Table S11).Malnutrition status -calculated for children aged<5 years of age.IQR -Interquartile range; Data were missing for the following variables: baseline parasitaemia (56 patients in 90% group and one patient in the <90% group), baseline haemoglobin (61 patients in 90% group and 2 patient in the <90% group), weight (54 patients in 90% group and 2 patient in the <90% group), fever at baseline (183 patients in the 90% group and 3 patients in <90%), vomiting (992 patients in the 90% group and 24 patients in <90% ).Malnutrition status -calculated for children aged<5 years of.
et al, Effect of adherence to primaquine on the risk of Plasmodium vivax recurrence: A WorldWide Antimalarial Resistance Network systematic review and individual patient data meta-

Figure S1 .
Figure S1.Study sites for clinical trial -Africa Region Figure S2.Study sites for clinical trial -Americas Region Figure S3.Study sites for clinical trial -Asia-Pacific Region TableS4.Comparison of baseline characteristics between included and targeted studies investigators of eligible studies were invited to share individual patient data and any additional data from eligible unpublished studies.Key terms A literature search (conducted March 3, 2020) with the following key terms was performed (version undertaken in Pubmed): Vivax AND (artefenomel OR arterolane OR amodiaquine OR atovaquone OR artemisinin OR arteether OR artesunate OR artemether OR artemotil OR azithromycin OR artekin OR chloroquine OR chlorproguanil OR cycloguanil OR clindamycin OR coartem OR dapsone OR dihydroartemisinin OR duo-cotecxin OR doxycycline OR halofantrine OR lumefantrine OR lariam OR malarone OR mefloquine OR naphthoquine OR naphthoquinone OR piperaquine OR primaquine OR proguanil OR pyrimethamine OR pyronaridine OR proguanil OR quinidine OR quinine OR riamet OR sulphadoxine OR tetracycline OR tafenoquine).

Figure S1 .
Figure S1.Study sites for efficacy studies -Africa Region Blue -included; Yellow -targeted but not included.

Figure S4 :
Figure S4: Adjusted risk of recurrence between days 7 and 90 in patients with information on supervision Shaded regions represent the 95% CIs.Age, sex, planned primaquine total dose and baseline parasitaemia were set at baseline mean or prevalence.Assumes zero effect from study site.

Table S12 :
Demographic and baseline characteristics for adherence by actual dosing 5Indicate if a protocol exists and where it can be accessed.If available, provide registration information including registration number and registry name.Provide publication details, if applicable. 10 If applicable, describe methods of standardising or translating variables within the IPD datasets to ensure common scales or measurements across studies.
12Describe methods used to assess risk of bias in the individual studies and whether this was applied separately for each outcome.If applicable, describe how findings of IPD checking were used to inform the assessment.Report if and how risk of bias assessment was used in any data synthesis.Appendix Specification of outcomes and effect measures 13 State all treatment comparisons of interests.State all outcomes addressed and define them in detail.State whether they were pre-specified for the review and, if applicable, whether they were primary/main or secondary/additional outcomes.Give the principal measures of effect (such as risk ratio, hazard ratio, difference in means) used for each outcome.12 Synthesis methods 14 Describe the meta-analysis methods used to synthesise IPD.Specify any statistical methods and models used.Issues should include (but are not restricted to): In order to collect data, we updated a comprehensive systematic review undertaken in 2017 [10] of all the prospective P. vivax clinical efficacy studies.We searched MEDLINE, Web of Science, Embase, and Cochrane Database of Systematic Reviews, according to the Preferred Reporting Items for Systematic Reviews and Meta-

Table S2 .
Reasons for studies not being included in analysis

Table S4 .
Comparison of baseline characteristics between included and targeted studiesThe studies with no information on adherence were not included in this column (n=3).†Multinational studies were allocated to the multiple regions, resulting in 37 studies based on region; 5 studies are multinational.# Median age was not available for 26 studies.*Percentage of female was not available for 8 studies.

Table S5 .
Distribution (number and percentage) of patients in adherence categories by study for (A) supervision, (B) total mg/kg dose administered

Table S6 :
Risk factors for Plasmodium vivax recurrence between days 7 and 90 in patients with information on supervision

Table S7 .
Sensitivity analyses for effect of adherence by supervision on Plasmodium vivax recurrence between days 7 to 90 restricted to randomised studies or observational studies

Table S8 .
Sensitivity analysis for effect of adherence by supervision on Plasmodium vivax recurrence between days 7 to 90 † -All study sites; Sensitivity analysis was generated by removing each study site one at a time (total of 70 sites).*The coefficient of variation calculated as standard deviation divided by the mean of the estimates.

Table S9 :
Demographic and baseline characteristics for adherence by total mg/kg dose administered Adherence by total mg/kg dose administered (%) Interquartile range; Data were missing for the following variables: sex (1 patient in the 90% group); fever at baseline (406 patients in the 90 group, 15 patients in >50-<90% and 57 patients in 50%), baseline parasitaemia (49 patients in 90% group and 15 patient in the 50% group), baseline haemoglobin (173 patients in 90% group, 6 patients in >50-<90% group and 58 patient in the 50% group), weight (56 patient in the 50% group).Malnutrition status -calculated for children aged<5 years of age.

Table S10 :
Risk factors for Plasmodium vivax recurrence between days 7 and 90 in patients with information on total mg/kg dose administered

Table S11 .
Sensitivity analysis for effect of adherence by total dose (mg/kg) administered on P. vivax recurrence between days 7 to 90

Table S12 :
Demographic and baseline characteristics for adherence by actual dosingAdherence by actual dosing (%) Data are presented as median (IQR) for continuous measures, and n (%) for categorical measures.